by Catalina Camia, USA TODAY

by Catalina Camia, USA TODAY

WASHINGTON - Thom Tillis won the GOP Senate nomination in North Carolina on Tuesday, delivering a big win to establishment Republicans over Tea Party insurgents.

Tillis, speaker of the North Carolina House, easily got over the 40% threshold needed to avoid a runoff in the closely watched Senate primary. His nomination sets up a fall matchup against Democratic Sen. Kay Hagan, in one of the races that could decide which party controls the Senate.

Republicans need a net gain of six Senate seats to oust Democrats from power.

"I want to go to Washington and clean up Kay Hagan's mess," Tillis told his enthusiastic supporters in Charlotte.

"If we want to change the mess of Obamacare, we have to change our senator," he said. "If we want to end the government's overreach, we have to change our senator."

Hagan, who easily was renominated for a second term, said her battle with Tillis would come down to who could best help the middle class.

"This election is a simple choice between two very different records," she said in a statement. "Thom Tillis has spent his time in Raleigh pushing a special-interest agenda that has rigged the system against middle-class families ... This is not an agenda that works for working families, and his priorities are out of sync with our common-sense North Carolina values."

The North Carolina Senate race was the first primary contest pitting the Tea Party and grass-roots conservatives vs. mainstream Republicans. The skirmishes will continue in coming weeks as Georgia, Kentucky, Idaho and Mississippi voters go to the polls to pick Republican nominees for Congress.

Going into Tuesday's primary, all eyes were on Tillis, obstetrician Greg Brannon and Baptist minister Mark Harris. Brannon had the support of Tea Party favorite Rand Paul, a Kentucky senator who is considering a 2016 presidential bid. Harris was backed by former Arkansas governor Mike Huckabee, a favorite of religious conservatives.

Brannon was coming in second to Tillis in the eight-person GOP field as results were being reported by the Associated Press. After Tillis was declared the winner, Paul pledged his support to the nominee on Facebook and wrote that it was "time for our side to unite" to defeat Hagan.

Tillis had the support of such big-name Republicans as Mitt Romney and Jeb Bush, and was aided by groups such as the U.S. Chamber of Commerce and American Crossroads, the super PAC co-founded by GOP strategist Karl Rove.

A runoff would have been a "scary scenario" for Tillis, said Kenneth Fernandez, an assistant professor of political science and director of the Elon University Poll. Fernandez said another round of voting would have forced Tillis to spend more money during the summer, when little attention is being paid to politics.

Republicans and their big-spending allies hope to avoid a repeat of 2012 when missteps by GOP candidates caused them to lose winnable races in Missouri and Indiana that prevented the party from winning the Senate majority.

"Tillis is the candidate best positioned to defeat Sen. Hagan in November, and he provides a clear contrast on issues important to our members," said Rob Engstrom, national political director for the U.S. Chamber. "We welcome that debate" over who can best promote economic growth in the state.

Steven Law, president and CEO of American Crossroads, called Tillis a "proven conservative" who can defeat Hagan. "We intend to hold her accountable for the mess she and Obama have made for North Carolina families in Washington," he said.

Before the primary, Hagan's campaign sent a mailer ahead that said Tillis once called Obamacare a "great idea," which was clearly intended to rankle conservatives.

That snippet is from a radio interview in February in which Tillis discussed ways to repeal the Affordable Care Act. PolitiFact noted that Tillis' full quote was: "The majority of the stuff that is in Obamacare is bad, because it's not fiscally sustainable. It's a great idea that can't be paid for."